Foreign objects are often introduced inside commercial and military aircraft during manufacturing or modifications. Items such as tools, fasteners, drill shavings, manufacturing material, personal objects, and debris may be inadvertently left inside the aircraft once the manufacturing or modification is complete.
For example, when co-drilling aircraft skins with their mating backing structure during manufacturing, foreign objects in the form of drill shavings are produced. Due do the forces from the drilling operations and due to the tendency for the chips to fall to the floor, drill shavings can potentially fall into gaps between the skin and the backing structure. It is often desirable to install fasteners into the newly drilled holes while the components are still held together in the drilling machine. Because of the potential presence of the stray drill shavings, the fasteners cannot be installed until an inspection is performed to ensure no foreign object debris (FOD) is present in the interface between the skin and the backup structure.
Moreover, during the skin installation operation of many aerospace structures, temporary fasteners are typically used to hold the skin to underlying ribs during fastener installation. If the operation is performed incorrectly, the holes in the underlying structure and skin can be misaligned, resulting in drilling or reaming of the hole which subsequently causes it to become oversized. Oversized holes reduce the intended properties of the fastened structure and may even produce accelerated in-service damage. This unfortunate opportunity also exists during original maintenance of the aircraft.
The presence of FOD in an aircraft is undesirable. FOD may interfere with the proper operation of critical aircraft systems. For example, FOD may foul cables or other mechanical devices that are used to control flight surfaces. FOD may also cause electrical shorts. Drill shavings can also cause discrepancies between structural surfaces, thereby increasing localized stresses and leading to crack sites or corrosion start points. Such undesirable effects of FOD may be costly and dangerous. It may inhibit proper operation of the aircraft to the point of causing a failure. Accordingly, during manufacturing operations the structure may have to be disassembled and time-consuming visual inspection performed in order to see if any FOD is present and often times no FOD is found or it is only found in very limited areas.
According to contemporary practice, for example as set forth in U.S. Pat. No. 7,463,714, technicians may inspect work areas of aircraft with two-dimension (2D) and/or three-dimension (3D) X-ray backscatter systems. Such systems are however expensive and usually produce large amount of data to be processed in order to identify FOD or other discrepancies in the aircraft.
As a result, it would be desirable to have a system for identifying FOD or other discrepancies in the aircraft which is not as expensive as, and/or produces data faster than contemporary two-dimension (2D) and/or three-dimension (3D) X-ray backscatter systems.